1. Field of the Invention
The present invention relates to an anti-vibration structure of an imaging device or observation device.
2. Related Background Art
Photographing while walking or on a traveling vehicle imparts vibration to a camera and renders a photographed image unobservable. Photographing from a vibrating location similarly results of vibration in an image and does not produce a useful image. These results are even more dramatic as the focal distance of a lens system increases.
Prior art approaches to preventing image vibration are as follows. An inclination angle of the optical system, that is, vibrations of the optical system are detected to eccentrically displace a portion of the lens system. Another approach is to have two optical elements of different thicknesses, which satisfy predetermined parameters arranged in a light path of the imaging lens and the image vibration is prevented by displacing the optical element (Japanese Patent Publication No. 26930/1984). However, in the former method, a light intensity changes with eccentricity, and in the latter method, since at least one of the optical elements is placed in front of the lens system, the optical element must be larger than the diameter of a front lens. As a result, the optical system is large and heavy. It has been proposed to compensate for the image vibration by controlling an apex angle of a liquid prism. However, by nature of its structure, a compensation angle is small, and chromatic aberration occurs as the angle increases because the prism is used.
For the method for optically preventing the image vibration, a gyroscope is used in the imaging device having the anti-vibration device so that the camera is always fixed along a direction of gravity, or a motor-driven universal head on which the camera is mounted is driven in accordance with an acceleration or angular velocity detected by an acceleration sensor ("Servo Type Camera Anti-Vibration Device" NHK Technical Journal, vol. 27, No. 11, pages 23-28 (1984)).
In this method, the light intensity does not vary, the weight of the optical system is not heavy and the chromatic aberration does not occur, unlike the method for optically preventing the image vibration. However, in the camera used in the proposed method, since the camera body including the imaging lens as well as a control unit in the camera is driven, the overall imaging device including the anti-vibration device is large and it cannot be used for hand-held photography.
The present applicant has proposed an anti-vibration camera in which an imaging lens device including an imaging lens system and photo-sensing means for sensing a light transmitted through the imaging lens is rotatably mounted on a camera body, and control means is provided to drive the imaging lens in accordance with an output of detection means which detects a vibration of the camera to compensate for the vibration.
The proposed anti-vibration camera has the following advantages.
(1) Since it is not necessary to eccentrically displace a portion of the lens system or insert a prism, an optical performance such as intensity and chromatic aberration is not deteriorated. A range of compensation is wide.
(2) Since the elements to be driven are only the lens system and the photoelectric conversion elements, a power of the drive system may be small and the camera is compact and of light weight.
(3) Since the camera is compact, hand-held photography with a long focal distance lens is permitted, and vibration-free stable image is produced by the hand-held photography while walking, and a vibration-free stable image is also produced by photographing on a traveling vehicle or from a vibrating location. Even a biginner of hand-held photography can produce an image which is substantially free from vibration.
However, the lens system has a fairly large moment of inertia although it is light in weight compared to the overall camera device. Accordingly, the drive system cannot follow a small amplitude vibration component, particularly that which has a high frequency, and the use of the device is limited to certain circumstances. For a large amplitude vibration, similar restriction is imparted because an operable range of the drive system is limited by its structure. Thus, the antivibration means has not been sufficient for the image vibration which includes high and low frequency components.